Changing fliuds with high miles

I owned a 86 (i think) Arostar van back in the early 90`s, i went thru 3 trans in the few short years i had it and swore i would never own another Ford auto trans as long as as i live. Well now i have three.

I bought my wife a Expedition in 2000 new, got my 16 year old a 94 Exlporer 4x4 with 190,000 miles, and just wrecked my Chevy and picked up a 99 F150 4x4 with 150,000 miles a few weeks ago. So far all shift and run perfect.

With my wife`s truck at 100,000 miles the trans as been serviced, but with the others i bought them with high miles. When i took the Explorer to a mechanic i really trust he told me not to touch the fluid. He said after changing the fluid the truck might not pull at all again.

I would really like some sound advise, would dropping the pan and changing the filter and adding more new fluid hurt the trans? The F150 is still good and red, were the Explorer is a little darker.

Welcome to this forum! Transmission fluid isn't made to last forever. Filters eventually get clogged. You should replace them before you start having problems.

i wouldnt recommend flushing it, because that just kicks up particles and the valve body isnt the best in the world. dropping the pan, changing the filter, and putting new fluid in it is, like brooklyn said, preventative maintenance.

The issue is that high mileage unchanged fluid is indicative of the probable presence of gunk and sludge accumulations within the tranny. (these normally stay in suspension and get drained out when you change the fluid... but old fluid has the detergent "used up" and these settle out in various places within the tranny.)

ATF contains a high level of detergent. When you completely change old fluid by "flushing" (which is sort of a misnomer as there is no agitation action in the procedure, any more than dialysis is a flushing of the human blood stream)
you have now introduced high detergent levels into a very dirty transmission - and a lot of thhat crud can come back into the fluid, causing clogging in the valve body - which is a pretty precise array of valves etc.

It is kind of a conundrum. Do I? don't I?

I have two suggestions... first is to do a pan drop fluid change. This only changes about 25-30% of the fluid. You are not introducing as much detergent when you do this. At the same time change the filter. Also add a bottle of lubegard platinum. This will help renew the friction properties of the fluid - which is a key part of the function of the fluid.

Then several months later, do it again. If the filter looks ok, you can re-use it this time.

Then finally several months later do it one last time - and change the filter as well.